1. Field of the Invention
The present invention relates to an apparatus and method for controlling the radiation of electromagnetic wave. More particularly, the invention relates to a technique for preventing the radiation of electromagnetic wave to a specific region.
2. Description of the Related Art
High level safety needs to be secured in a spacecraft and a manned space station, and it is demanded that the electromagnetic wave emitted from an antenna on the spacecraft should have the electric field strength of 100 V/m or less with respect to human. However, the main lobe of each antenna is usually greater than 100 V/m. Therefore, various measures are taken to attain the safety required. For example, mechanical stoppers of the antenna pointing mechanism are attached for the windows of the manned spacecraft. The following techniques are known for eliminating the influence of the radiation of electromagnetic wave.
For example, in xe2x80x9cApparatus for Preventing Radiation Hazardxe2x80x9d disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 9-257914), a reception antenna is provided at a place such as a staying location of a human being where harmful microwave should be not applied, to detect microwave. When the antenna receives the microwave, the radiation of the microwave from a radar apparatus is stopped, thereby protecting human being from the radiation of microwave.
Also, in xe2x80x9cApparatus for Preventing Radiation Hazardxe2x80x9d disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-83987), a means for detecting radiation of microwave to a staying place of the human being is provided to monitor the radiation of the microwave. When the microwave is detected, the operation of only the radar apparatus as a radiation source is stopped. If the microwave emitted from any external source is detected, this fact is notified to the external source. In this method, any radar apparatuses other than the radar apparatus which erroneously radiates the microwaves are not stopped, though the microwave are detrimental to man.
Further, Japanese Patent No. 2910619 discloses xe2x80x9cSystem for stopping Power Supply for Radio Transmissionxe2x80x9d. The system is applied to a radio communication system in which data is transmitted in two ways between the first and second radio communication apparatuses of the same structure, by use of signals having a frequency higher than the microwave-band frequency. More specifically, the first radio communication apparatus receives the signal from the second radio communication apparatus and detects the level of the signal. When the first radio communication apparatus detects that the level of the signal received has remained equal to or below a predetermined value and the state of the low reception signal level continues longer than a predetermined time, the power supply to the second radio communication apparatus is interrupted. Thereafter, the power is intermittently supplied to the second radio communication apparatus for every prescribed period. At this time, when the level of the reception signal exceeds a predetermined value, power is then continuously supplied to the second radio communication apparatus. Thus, in the bidirectional radio communication system in which microwave or electromagnetic wave of shorter wavelength is used, the transmission output of the radio communication apparatus can be automatically stopped, when there is high possibility that people are exposed to the electromagnetic wave. This protects human being from the radiation of electromagnetic wave.
It should be noted that in xe2x80x9cAircraft Radar Apparatusxe2x80x9d disclosed in Japanese Laid Open Utility Model application (JU-A-Showa 60-145378), while a aircraft stays on the ground, a signal representing an EL angle of an antenna on the aircraft is inputted into a radar apparatus. When the signal indicates that the EL angle has become smaller than a preset value, the high power radiation of the electromagnetic wave from the antenna is suppressed. Hence, the ground staff can inspect and repair the radar apparatus, without being influenced by the electromagnetic wave.
Also, in xe2x80x9cMobile Communication Apparatusxe2x80x9d disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-70504), the mobile communication apparatus is composed of an antenna, a tracking unit, a receiver, a transmitter, a handset, and a control unit. The antenna receives and transmits electromagnetic wave. The tracking unit directs the antenna to the coming electromagnetic wave. The receiver demodulates the electromagnetic wave. The transmitter modulates data to be transmitted into electromagnetic wave. The handset displays data to the user and receives instructions from the user. The control unit controls the tracking unit, receiver, transmitter and handset. The control unit, which is essential to the apparatus, is composed of measurement means, display means, and hazard inferring means. These means quickly solve reception troubles that may frequently take place in the communication section provided in the mobile communication apparatus.
As described above, mechanical stoppers are attached to the windows of a spacecraft to attain the safety required in the spacecraft. Whether or not electromagnetic wave from the antenna is radiated to the other parts of the spacecraft, which are provided with no stoppers, is determined by means of software control. Therefore, various design requirements must be fulfilled to enhance the safety in the spacecraft.
It should be noted that xe2x80x9cApparatus for Preventing Radiation Hazardxe2x80x9d disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 9-257914) and xe2x80x9cApparatus for Preventing Radiation Hazardxe2x80x9d disclosed Japanese Laid Open Patent Application (JP-A-Heisei 11-83987) have an antenna for detecting electromagnetic wave, which is specially provided. Consequently, the apparatus is complex and the manufacturing cost of the apparatus is high.
Also, in xe2x80x9cSystem for Interrupting Power Supply to Radio Transmittersxe2x80x9d disclosed in Japanese Patent No. 2,910,619, whether electromagnetic wave should be radiated or not is determined in accordance with the level of a signal received by the antenna and the period for which the signal remains at the level. Therefore, it cannot be said that the safety is sufficient.
Therefore, an object of the present invention is to provide an apparatus and method for controlling the radiation of electromagnetic wave, which have a simple structure and is realized at low cost.
Another object of the present invention is to provide an apparatus and method for controlling the radiation of electromagnetic wave, which can yet serve to accomplish sufficient safety.
In order to achieve an aspect of the present invention, a electromagnetic wave radiation control apparatus includes an antenna, a modulator, an amplifier, and a radiation control unit. The modulator modulates a carrier wave based on a transmission signal to output a modulated signal, wherein the modulator stops the output of the modulated signal in response to a power off command. The amplifier amplifies the modulated signal such that the amplified signal is radiated as electromagnetic wave from the antenna, when the modulated signal is outputted from the modulator. The radiation control unit generates the power off command to the modulator, when radiation of electromagnetic wave in a current radiation direction of the antenna is inhibited, or when a level of a reception signal by the antenna is equal to or lower than a predetermined minimum level.
Here, the radiation control unit includes a data processor which outputs the power off command in response to an error signal, and a control unit. The control unit generates the error signal to the data processor, when radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, or when the reception signal level by the antenna is equal to or lower than the predetermined minimum level. In this case, the control unit may include a blocking state determining unit, a lock status determining unit and a logic circuit. The blocking state determining unit generates a blocking error signal when radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited. The lock status determining unit generates an unlock signal when the reception signal level is equal to or lower than the predetermined minimum level. The logic circuit generates the error signal based on the blocking error signal and the unlock signal.
Also, the radiation control unit may further generate a high voltage power off command to the amplifier, when the amplified signal is outputted from the amplifier in a state in which the power off command can be generated. The amplifier stops an operation thereof in response to the high voltage power off command such that the amplified signal is not outputted to the antenna. The radiation control unit generates the high voltage power off command to the amplifier, when the radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, and when the amplifier outputs the amplified signal. The radiation control unit may include a data processor and a control unit. The data processor outputs the power off command in response to an error signal. The control unit generates the error signal to the data processor, when radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, or when the reception signal level by the antenna is equal to or lower than the predetermined minimum level, and the high voltage power off command to the amplifier, when the amplified signal is outputted from the amplifier in the state in which the radiation of electromagnetic wave in said current radiation direction of said antenna is inhibited. In this case, the control unit may include a blocking state determining unit, a lock status determining unit and a logic circuit. The blocking state determining unit generates a blocking error signal when radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, and the high voltage power off command to the amplifier, when the amplified signal is outputted from the amplifier in the state in which the radiation of electromagnetic wave in said current radiation direction of said antenna is inhibited. The lock status determining unit generates an unlock signal when the reception signal level is equal to or lower than the predetermined minimum level. The logic circuit generates the error signal based on the blocking error signal and the unlock signal.
Another aspect of the present invention is directed to a method of controlling radiation of electromagnetic wave in which a spacecraft which includes an antenna, a modulator which modulates a carrier wave based on a transmission signal to output a modulated signal, and an amplifier which amplifies the modulated signal such that the amplified signal is radiated as electromagnetic wave from the antenna, when the modulated signal is outputted from the modulator. The method is attained by (a) determining whether radiation of electromagnetic wave in a current radiation direction of the antenna is inhibited; by (b) determining a level of a reception signal by the antenna is equal to or lower than a predetermined minimum level; and by (c) generating a power off command to the modulator such that the modulator stops the output of the modulated signal to the amplifier, when the radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, or when the reception signal level is equal to or lower than the predetermined minimum level.
The (c) generating may be attained by (d) generating an error signal to the data processor, when the radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, or when the reception signal level by the antenna is equal to or lower than the predetermined minimum level; and by (e) generating the power off command in response to the error signal. In this case, the (d) generating may be attained by generating a blocking error signal when the radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited; by generating an unlock signal when the reception signal level is equal to or lower than the predetermined minimum level; and by generating the error signal based on the blocking error signal and the unlock signal.
Also, the (c) generating may further includes: generating a high voltage power off command to the amplifier such that the amplifier stops an operation thereof in response to the high voltage power off command, when the amplified signal is outputted from the amplifier in a state in which the power off command can be generated. In this case, the (c) generating may be attained by generating the high voltage power off command to the amplifier, when the radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, and when the amplifier outputs the amplified signal.
Also, the (c) generating may be attained (f) generating an error signal to the data processor, when radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, or when the reception signal level by the antenna is equal to or lower than the predetermined minimum level, and the high voltage power off command to the amplifier, when the amplified signal is outputted from the amplifier in the state in which the radiation of electromagnetic wave in said current radiation direction of the antenna is inhibited; and by (g) generating the power off command in response to an error signal. In this case, the (f) generating may be attained by generating a blocking error signal when radiation of electromagnetic wave in the current radiation direction of the antenna is inhibited, and the high voltage power off command to the amplifier, when the amplified signal is outputted from the amplifier in the state in which the radiation of electromagnetic wave in said current radiation direction of said antenna is inhibited; by generating an unlock signal when the reception signal level is equal to or lower than the predetermined minimum level; and by generating the error signal based on the blocking error signal and the unlock signal.